Just a thought here.. How many insert effects can the PSR-2100 run at the same time? Have you tried turning off the "voice set" feature??? When you select a voice effects are automatically chosen for the voices and so on.. I know that since my PSR-550 only handles one insert effect at a time, in order for to avoid conflicting DSP problems I always turn off the voice set before I record... Meaning I choose my own effects manually..... I'm not sure if this is the problem with your 2100, but thought I'd mention this.. Again for the possibility that you maybe exceeded the DSP limitations as it relates to insert effects.. As far as the crackling actually being in the recording, that's a fault of the keyboard.. Could be a loose wire connection somewhere or even something with the motherboard.. I can understand if you're gettting it just from the speakers, but if it's actually recording into the music means the problem is deeper than that. Have you tried using an external set of speakers to play back the songs to see if the sound is there?
Squeak
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GEAR: Yamaha MOXF-6, Casio MZX-500, Roland Juno-Di, M-Audio Venom, Roland RS-70, Yamaha PSR S700, M-Audio Axiom Pro-61 (Midi Controller). SOFTWARE: Mixcraft-7, PowerTracks Pro Audio 2013, Beat Thang Virtual, Dimension Le.